Drug administration by injection has been widely used for injection of a drug such as vaccine into the body. Although injection is a highly safe method for administration, it often causes severe pain since an injection needle is deeply pierced into the body to deliver the drug into the subcutaneous tissue. Further, particularly in developing countries, there are many issues such as infection by reuse of injection needle and needle stick accidents.
Therefore, as an alternative drug administration method to injection, attention has been paid to use of an array of a plurality of needle members of micron order to pierce the skin for direct administration of a drug into the skin. According to this method, it is possible to almost avoid producing pain during piercing into the skin since the length of the needle members is controlled not to reach the nerve cells in the dermis layer. Moreover, a drug can be intradermally administered in a convenient manner without using a special tool for drug administration (see PTLs 1 and 2).
Further, when vaccine is intradermally administered using the needle members, the amount of vaccine used can be reduced compared with subcutaneous injection since antigen presenting cells are abundant in the skin.
The needle member must have a thinness and sharpness sufficient for puncturing the skin and a length sufficient for intradermal drug delivery. Accordingly, the needle member desirably has a diameter of several micrometers to several hundreds of micrometers and a length that penetrates through the stratum corneum which is the outermost layer of the skin but does not reach the nerve fibers, which is specifically several tens of micrometers to several hundreds of micrometers.
Materials for the needle member are required to be harmless to the human body even if the needle member is broken and left in the body. For such materials, biocompatible resins such as medical grade silicone, maltose, polyglycolic acid, polylactic acid, and dextran are regarded as promising materials (see PTL 3).